UN 1805 — Phosphoric acid, solution
Placard: Corrosive. ERG Guide 154. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Phosphoric acid, solution, is a widely used chemical in various industries, including food, pharmaceuticals, and water treatment. It is classified as a DOT Class 8 material, indicating it is toxic and/or corrosive. First responders may encounter phosphoric acid during transportation accidents, industrial spills, or fires. The scale of production and transport of phosphoric acid is significant, with millions of tons produced annually. Phosphoric acid is a clear, colorless to pale yellow viscous liquid with a faint acidic odor. It is essential for first responders to be aware of the hazards associated with phosphoric acid and take necessary precautions to ensure a safe response. Phosphoric acid is used in various applications, including the manufacture of fertilizers, detergents, and pharmaceuticals.
Hazard overview: Phosphoric acid is toxic and/or corrosive, and inhalation, ingestion, or skin contact with the material may cause severe injury. Contact with molten substance may cause severe burns to skin and eyes. Fire may produce irritating, corrosive, and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental damage. The LC50 value for phosphoric acid is not well-established, but it is known to be highly toxic. The IDLH value is also not well-established, but it is recommended to use SCBA in concentrated vapors or confined spaces. Phosphoric acid has a low volatility, and its vapor density is not applicable. However, it can still pose a significant hazard due to its corrosive nature.
Response guidance: In the event of a phosphoric acid spill, it is essential to isolate the area, with a small spill requiring a 30m isolation zone in all directions, and a large spill requiring a 100m isolation zone and 300m downwind during the day or 800m at night. Evacuation zones should be established, and correct suppression agents, such as water spray, dry chemical, or CO2, should be used. Decontamination is crucial, and CHEMTREC should be contacted in case of an emergency. First responders should be aware of the potential for phosphoric acid to react with water, generating heat, and take necessary precautions to avoid any violent reactions.
Firefighter training notes: First responders should be trained to respond to phosphoric acid spills and fires, with a focus on isolation, evacuation, and suppression. A known tactical error for this chemical class is the use of incorrect suppression agents, which can exacerbate the situation. ICS position needs and mutual aid criteria should be established to ensure a coordinated response. First responders should be aware of the potential for phosphoric acid to react with water and take necessary precautions to avoid any violent reactions.
Regulatory context: Phosphoric acid is classified as a DOT Class 8 material, indicating it is toxic and/or corrosive. The OSHA PEL/TLV is not well-established, but it is recommended to follow the guidelines for toxic and corrosive substances. Phosphoric acid is not listed on the CERCLA list, but it can still pose a significant environmental hazard due to its corrosive nature.
Storage & handling: Phosphoric acid should be stored in a well-ventilated area, away from incompatible materials such as strong bases and reducing agents. The temperature limit should be below 50C (122F), and the container type should be compatible with the substance. The ventilation standard should be established to prevent the accumulation of toxic and corrosive vapors.
UN 1805 Quick Details
Common Hazards of UN 1805
- TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury
- Contact with molten substance may cause severe burns to skin and eyes.
- Avoid any skin contact.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental
- Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive
- Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.).
- Corrosives in contact with metals may evolve flammable hydrogen gas.
Chemical Identity & Physical Properties
Phosphoric acid is a clear, colorless to pale yellow viscous liquid with a faint acidic odor. It has a boiling point of 158C (316F) for an 85% solution, which varies with concentration. The flash point is not applicable, as it is a non-flammable aqueous solution. The vapor pressure is low, and the specific gravity is approximately 1.3-1.4, depending on the concentration.
| Also known as | Orthophosphoric acidH3PO4Phosphoric acid solutionWhite phosphoric acid |
| CAS Number | 7664-38-2 |
| Appearance | Clear, colorless to pale yellow viscous liquid. Odorless or has a faint acidic odor. Solution concentration typically ranges from 50-85%. |
| Flash Point | Not applicable (non-flammable aqueous solution) |
| Boiling Point | 158C (316F) for 85% solution; varies with concentration |
| Vapor Density | Not applicable (low volatility aqueous solution) |
| Water Reactivity | Miscible with water; dilution generates heat but no violent reaction |
Fireground Response Guidance — UN 1805
Extinguishing Media
PPE Requirements
A minimum of Level C PPE is required, including an acid-resistant suit, boots, gloves, face shield, and SCBA if concentrated vapors or confined spaces are present. The rationale for each item is to prevent skin contact and inhalation of toxic and corrosive substances. The suit material should be acid-resistant, and the glove specification should be compatible with the substance.
Isolation & Evacuation
First Actions for a UN 1805 Incident
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
📋 Copy & Share Field Card
UN 1805 — Phosphoric acid, solutionUse for: Quick radio or face-to-face size-up. Short, structured, field-ready.
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
Use for: Quick text to command or incoming units. Fits in a single SMS.